Science says the difference between a friend and a best friend comes down to two things

Friendship is more quantifiable than you think. Daxiao Productions/Shutterstock.com

Friends are important for health and happiness — but they don't just materialize out of thin air.

A new study suggests it takes 50 hours before an acquaintance becomes a casual friend; 90 before they become a friend; and more than 200 before they become a best friend.

During that time, conversations focus on catching up and meaningful issues — not small talk.

Teaching someone how to make friends is like teaching someone how to ride a bike — you say this, you put your foot here, do you get it now?

That is to say, it's all kind of intuitive: When it's working, you'll know.

But a new scientific paper, which was published in the Journal of Social and Personal Relationships and cited on Psychology Today, provides some more concrete direction for students in the school of friend-making.

According to the paper, you need to spend about 50 hours with someone before they go from an acquaintance to a casual friend, about 90 hours before they go from there to friend, and more than 200 hours before they become a best friend.

The research was led by Jeffrey A. Hall, a communications professor at the University of Kansas. Hall ran two studies: one with 355 adults who'd recently moved to a new place and one with 112 college first-years.

In the first study, Hall asked participants to think of someone new they'd met since moving. Participants described how much time they spent together, how close they felt to that person, and where the person fell on a scale from acquaintance to best friend.

In the second study, Hall asked participants to think of two new acquaintances and then followed up with the students twice over the first nine weeks of the academic year. At each point, students indicated how much time they'd spent with the acquaintances and how they characterized their friendship.

Results showed that the more time people spent together, the closer they were. But it wasn't simply occupying the same physical space that seemed to cinch the deal.

If you're trying to make a friend, engaging in small talk won't cut it

In fact, Hall found that spending a lot of time together at work or at school predicted less friendship closeness. On the other hand, "hanging out" together, watching TV or playing games, outside these realms predicted greater friendship closeness.

The content of people's conversations turned out to matter a lot, too. People who engaged in a lot of small talk wound up getting less close over time. By contrast, people who spoke more substantively: "catching up, checking in, joking around, and meaningful conversation."

That finding jibes with other research on the importance of self-disclosure in the early stages of friendship: Revealing details about your life (slowly and selectively) can help strengthen the bond between you and another person.

It's worth noting here that the link between how much time people spent together and how close they became is correlational. It's possible that people were inclined to hang out because they clicked — not that they clicked because they hung out.

Also worth noting: Some people may simply be better equipped to make friends than others. Research suggests that people who are agreeable, open to experience, and conscientious are more likely to experience " friendship chemistry," or an instant connection.

Ultimately, this research suggests that making a friend means making a substantial investment of time and energy. Neither of those are unlimited resources, which may be why most of us can count the number of close pals we have on one hand.